In an image forming apparatus, such as a laser printer, a known paper discharge method is used when one surface of paper (sheet) is printed. The method is capable of carrying out a face-down paper discharging operation in which the paper is discharged with a printed surface facing downward, and a face-up paper discharging operation in which the paper is discharged with a printed surface facing upward. This method is configured so that how to discharge the paper can be selectively determined depending upon the material and sizes of the paper, An image forming method is also known having the double face printing function of forming an image on both surfaces of paper in addition to the above-mentioned function.
There is an apparatus as an example of such an image forming apparatus disclosed in JP-A-2002-104707. In order to carry out a face-down paper discharging operation after an upper surface of paper 100 is printed as shown in FIG. 11, the paper 100 is sent from paper fixing and discharging rollers 102, on which the paper is provided in a fixing unit 101, to upper paper discharging rollers 103 provided in an upper portion of an apparatus body, and the paper 100 is discharged with a printed surface thereof directed downward onto a paper discharging tray 104 on an upper surface of the apparatus body. In order to carry out a face-up paper discharging operation, a rear-side cover 105 in a rear wall of the apparatus body is opened, and the paper 100 is sent rearward from the paper fixing and discharging rollers 102, the paper being then discharged with the printed surface directed upward onto the opened rear cover 105. In order to carry out a double face printing operation, the paper 100 the printing of one surface of which has been completed is once sent from the paper fixing and discharging rollers 102 to the upper paper discharging rollers 103, and the upper paper discharging rollers 103 are reversely rotated before a rear end of the paper 100 passes the upper paper discharging rollers 103, so that the rear end of the paper 100 is sent out to a re-transfer passage 106 provided so as to extend from an inner side of the rear-side cover 105 toward a front portion of the apparatus, the other surface of the paper 100 being then printed